Shelf unit



FIG. 1 is a front elevational view of the shelf unit showing our new design, the rear view being a mirror image thereof;

FIG. 2 is an end elevational view, the opposite end being identical thereto;

FIG. 3 is a top plan view thereof; and

FIG. 4 is a bottom plan view thereof. 

The ornamental design for a shelf unit, as shown and described. 